An aqueous solution of H-2[PtCl6]. 6 H2O reacts with crown ether 18-crown-6 to give [H3O6][PtCl5(H4O2)]. 2(18-cr-6) (1) and (H3O)(2)[PtCl6]. 2(18-cr-6) (2a). In the presence of HCl, only 2a is formed; in an analogous manner, (H3O)(2)[PtCl6]. 2(15-cr-5). 2 H2O (2b) and (H3O)(2)[PtCl6]. 2(DCH-18-cr-6) (2c) were obtained. 1 is gradually decomposed in water to give [PtCl4(H2O)(2)].(18-cr-6).2H2O (3). 1-3 were characterized by microanalysis and IR and NMR spectroscopy (H-1, C-13, Pt-195). The X-ray structure analysis of 1 (orange needles; space group P212121, a = 7.938(1) Angstrom, b = 15.691(2) degrees, c = 34.861(4) Angstrom; Z = 4) shows an anionic entity [PtCl5(H4O2)](-) and a cationic entity [H13O6](+) which are separated by a crown ether molecule 18-cr-6. The [H13O6](+) cations exhibit the structure [H3O(H4O2)(2)(H2O)](+) and are also separatedby crown ether molecules in such a way that the crystal is threaded by chains built up of 18-Cr-6/[H13O6](+) units at which the 18-cr-6/[PtCl5(H4O2)](-) moieties are fixed as lateral branches. Thus, the cations [H13O6](+) are embedded in three crown ether molecules. All terminal hydrogens are involved in hydrogen bridges to oxygen atoms of the cronin ether molecules. The O-w ... O-w distances are distinctly longer in the mean than the O-w ... O-w distances within the [H13O6](+) moiety.